The use of intravascular medical devices and implants has become an effective method for treating many types of vascular disease. In general, a suitable intravascular device is inserted into the vascular system of the patient and navigated through the vasculature to a target site in a patient. Using this method, virtually any target site in the patient's vascular system may be accessed, including the coronary, cerebral, and peripheral vasculature.
Catheters are often utilized to place medical implants, such as stents and embolic devices, at a desired location within a body. Usually, stents are tubular prosthesis for insertion through body lumens; although, stents may have a wide variety of sizes and shapes. A stent may be delivered by being mounted over a balloon and loaded onto a catheter, and after positioning the stent at the desired location, the balloon is inflated to expand the stent radially outward. Alternatively, a stent may be loaded onto a catheter in a reduced configuration and/or diameter; then introduced into the lumen of a body vessel. For example, self-expanding stents are to be delivered in an elastically compressed or collapsed state while being confined within a tubular restraining member, such as a catheter. The catheter is threaded through the vascular system until its distal end reaches the implantation site. Additionally, the catheter may be introduced into the patient over a guidewire which has been previously introduced, in the so-called “over-the-wire” and “rapid-exchanged” delivery systems. The collapsed stent is mounted on or distally located from a pusher member disposed within the catheter, so that the stent is introduced, advanced or pushed through the catheter. When the stent is positioned adjacent to the desired location, it is pushed out of the catheter (i.e., unsheathed; which may include withdrawal of the catheter) and allowed to expand to a predetermined diameter in the body vessel, engaging the interior walls of the vessel, without requiring assistance from a balloon.
A self-expanding stent may be biased so as to expand upon release from the delivery catheter and/or includes a shape-memory component which allows the stent to expand upon exposure to a predetermined condition. Some stents may be characterized as hybrid stents which have some characteristics of both self-expandable and balloon expandable stents. In either stent configuration, once delivered to a target location within the body, the expanded or enlarged stent supports and reinforces the vessel wall while maintaining the vessel in an open and unobstructed condition.
Some stent delivery systems have the inability to protect the distal end of a self-expanding stent when the stent is pushed through a catheter. Other delivery systems include a retaining member that engages the distal end of the stent mounted on a pusher member. With some frequency, when the self-expanding stent is unsheathed and/or pushed out of the catheter in delivery systems having a retaining member, the distal end of the stent is undesirably held by the retaining member, so the stent is not allowed to expand and be deployed at the target location. Thus, there may be an increased risk of failure and duration of the medical procedure, or at least, a failure to deliver the stent in a target location, when the stent distal end is undesirably held by the retaining member after the stent is pushed out of the catheter or the catheter is unsheathed. Accordingly, there is an ongoing need to provide an implant delivery system for delivering self-expanding stents that preserves the integrity the distal end of the stent when pushed through a catheter for deployment, and provides a controlled delivery and release of the distal end of a self-expanding stent during deployment into a target location.